feat(epicardium): gpios are configurable as ADC

fixes #82 (closed)

The 3/4 of the Wristband's GPIOs have ADC as ALT1 mode. Just use it and be glad.

It's a bit wonky that WRISTBAND_3 is an exception here, but we can't change this.

epicardium/modules/gpio.c

 #include "epicardium.h"
 #include "gpio.h"
 #include "max32665.h"
+#include "mxc_sys.h"
+#include "adc.h"
 #include "mxc_errors.h"
+#include "modules/log.h"
 
 /*
  * Despite what the schematic (currently, 2019-08-18) says these are the correct
@@ -26,6 +29,14 @@ static gpio_cfg_t gpio_configs[] = {
 				    GPIO_PAD_NONE },
 };
 
+static int s_adc_channels[] = {
+	[EPIC_GPIO_WRISTBAND_1] = ADC_CH_5,
+	[EPIC_GPIO_WRISTBAND_2] = ADC_CH_6,
+	[EPIC_GPIO_WRISTBAND_3] =
+		-1, //AFAICT on P0.29, there is no ADC available
+	[EPIC_GPIO_WRISTBAND_4] = ADC_CH_4,
+};
+
 int epic_gpio_set_pin_mode(uint8_t pin, uint8_t mode)
 {
 	if (pin < EPIC_GPIO_WRISTBAND_1 || pin > EPIC_GPIO_WRISTBAND_4)
@@ -43,14 +54,27 @@ int epic_gpio_set_pin_mode(uint8_t pin, uint8_t mode)
 		if (mode & EPIC_GPIO_MODE_IN) {
 			return -EINVAL;
 		}
+	} else if (mode & EPIC_GPIO_MODE_ADC) {
+		if (s_adc_channels[pin] == -1) {
+			LOG_WARN("gpio", "ADC not available on pin %d", pin);
+			return -EINVAL;
+		}
+		cfg->func = GPIO_FUNC_ALT1;
+		if (mode & EPIC_GPIO_MODE_OUT) {
+			return -EINVAL;
+		}
 	} else {
 		return -EINVAL;
 	}
 
-	if (mode & EPIC_GPIO_PULL_UP) {
-		cfg->pad = GPIO_PAD_PULL_UP;
-	} else if (mode & EPIC_GPIO_PULL_DOWN) {
-		cfg->pad = GPIO_PAD_PULL_DOWN;
+	if (!(mode & EPIC_GPIO_MODE_ADC)) {
+		if (mode & EPIC_GPIO_PULL_UP) {
+			cfg->pad = GPIO_PAD_PULL_UP;
+		} else if (mode & EPIC_GPIO_PULL_DOWN) {
+			cfg->pad = GPIO_PAD_PULL_DOWN;
+		} else {
+			cfg->pad = GPIO_PAD_NONE;
+		}
 	} else {
 		cfg->pad = GPIO_PAD_NONE;
 	}
@@ -71,6 +95,8 @@ int epic_gpio_get_pin_mode(uint8_t pin)
 		res |= EPIC_GPIO_MODE_IN;
 	else if (cfg->func == GPIO_FUNC_OUT)
 		res |= EPIC_GPIO_MODE_OUT;
+	else if (cfg->func == GPIO_FUNC_ALT1)
+		res |= EPIC_GPIO_MODE_ADC;
 	if (cfg->pad == GPIO_PAD_PULL_UP)
 		res |= EPIC_GPIO_PULL_UP;
 	else if (cfg->pad == GPIO_PAD_PULL_DOWN)
@@ -106,6 +132,14 @@ int epic_gpio_read_pin(uint8_t pin)
 		return GPIO_OutGet(cfg) != 0;
 	} else if (cfg->func == GPIO_FUNC_IN) {
 		return GPIO_InGet(cfg) != 0;
+	} else if (cfg->func == GPIO_FUNC_ALT1) {
+		ADC_StartConvert(s_adc_channels[pin], 0, 0);
+		uint16_t value;
+		int rc = ADC_GetData(&value);
+		if (rc < 0) {
+			return -EIO;
+		}
+		return (int)value;
 	} else {
 		return -EINVAL;
 	}